1. Field of the Invention
The present invention is related to a technology of positioning a position using a radio signal. Especially, it is related to a technology of improving the convenience when the position of a mobile station is positioned using a global positioning system (GPS)
2. Description of the Related Art
Recently, an apparatus with a position-positioning function using GPS has become more and more widespread.
A GPS receiver (GPS positioning apparatus) for the position-positioning using a radio signal (hereinafter, referred to as “GPS signal”) that is transmitted from a satellite configuring the GPS has a system for the position-positioning at two or more dimensions with high accuracy using signals transmitted from, for example, three or more satellites from among the signals transmitted from about twenty-four satellites circulating around the earth. This GPS technology is also used in car navigation systems and PDAs (Personal Digital Assistant: portable type information communication devices for individual users). According to this technology, the position-positioning of a mobile station or a user is implemented.
Since the GPS receiver implements the position-positioning using a GPS signal, preferable position-positioning cannot be theoretically implemented in such an environment where the line-of-sight between a satellite and a mobile station (GPS receiver) is interfered. Accordingly, a mobile station cannot position its own position in a space which is not exposed to the sky, for example, indoors, in cars or the like and where a GPS signal cannot be directly received (hereinafter, referred to as a GPS signal non-receipt area) in a mobile station. Here, the sky indicates a range of about ±90 degrees to the zenith of a mobile station. Furthermore, the fact that a satellite exists in the sky indicates that the satellite exists (can be seen) in about ±90 degrees to the zenith of a mobile station if there is no obstacle in the way.
Regarding this technology, Japanese patent application laid-open publication No. 2000-111648 (hereinafter, referred to as [document 1]) discloses a technology such that a position ID oscillator for emitting infrared rays signal including position ID is provided indoors and a mobile station is configured to receive the radio wave from a satellite outdoors while it receives the infrared rays signal indoors, thereby enabling the position-positioning of a mobile station irrespective of whether the mobile station is indoors or outdoors.
In Japanese patent application laid-open publication No. 2003-57330 (hereinafter, referred to as [document 2]) discloses a technology of specifying the present position of a mobile station that is moving in a GPS signal non-receipt area by re-radiating a GPS signal to the GPS signal non-receipt area indoors, etc. and by radiating the pre-stored latitude and longitude data to this area using a position data transmission apparatus.
The following is the explanation of the outline of the positioning method using a GPS receiver.
A GPS receiver receives a GPS signal that is transmitted from a plurality of satellites with the same frequency. Each satellite generates a GPS signal based on a diffuse spectrum communication system using a pseudo random noise code having different code arrays. Therefore, the GPS receiver can receive and process with the same frequency the GPS signals that are transmitted from a plurality of satellites. Then, the GPS receiver calculates the attainment time of a signal from each satellite on the basis of the time when this pseudo random noise code is received. Meanwhile, the pseudo random noise code includes a C/A cord and a P cord (Y cord) that is kept confidential in order to restrict a user. The code that is generally disclosed is only C/A cord.
Furthermore, the GPS signal includes a navigation message in which the orbit information (ephemeris), the calendar (almanac), etc. of the satellite is shown together with the pseudo random noise code.
The almanac indicates orbit information about the outlines of all the satellites other than its own satellite that configure GPS, that is, the timetable of satellites. Accordingly, this information is used for determining a satellite that can be acquired by the GPS receiver. On the other hand, the ephemeris shows the exact position of its own satellite and it is this important information that is needed to calculate the position of a mobile station. The GPS receiver calculates the distance from each satellite using the attainment time of the signal from each satellite and then calculates the own position using those distances (at least three distances) and the orbit information about the satellites.
Furthermore, before receiving the GPS signal and starting the position-positioning, the GPS receiver selects the satellite that can be acquired during that period of time on the basis of the almanac received in the past. Subsequently, the GPS receiver implements a search operation for acquiring the signal from a satellite while subtly changing the clock frequency of the GPS receiver. This search operation usually requires several to several tens of seconds. However, in the case where the received almanac becomes old since the GPS receiver has not been used for a long time or in the case where the GPS receive is moved from the position where the positioning operation is previously implemented to the position that is far from the previous position, it takes a longer time since the GPS receiver automatically implements operations for acquiring all the satellites (it takes longer than twelve minutes and thirty seconds to receive all the almanacs).
Accordingly, in the case where the power of the GPS receiver is on and the almanac is kept old and not updated since the GPS receiver is positioned in a GPS signal non-receipt area for a long time, the initial positioning time requires a long time when the mobile station comes into a position where the GPS signal can be directly received.
Similarly, in the case where the power of the GPS receiver is on in the GPS signal non-receipt area and the ephemeris is kept old and not updated since the GPS receiver stays in the GPS signal non-receipt area for a long time, etc., the accuracy sometimes deteriorates at the time of the initial positioning.
Regarding this point, for example, Japanese patent application laid-open publication No. 7-280917 (hereinafter, referred to as [document 3]) discloses a technology of re-transmitting a GPS signal to a GPS signal non-receipt area so that the mobile station that moves in the GPS signal non-receipt area can be promptly positioned when the mobile station comes into a position where the GPS signal can be directly received. Additionally, this article discloses another technology of implementing maintenance, inspection, repair, etc. of the GPS receiver even indoors where the GPS signal cannot be received.
Meanwhile, the latest car navigation systems offer an apparatus for continuing the positioning of the own apparatus using a gyrocompass, a direction sensor, a distance sensor, etc. even in the position where such a GPS signal cannot be received.
The positioning method using a GPS receiver is described in detail, for example, in the following document. Jun Tsuchiya and Hiroshi Tsuji: “Foundation of new GPS measurement”, Japan Association of Surveyors, Sep. 30, 2002.
In the technology that is disclosed in the document 1, a reception unit for receiving the infrared rays signal including position ID is required so that the hard scale of a mobile station increases. Furthermore, position ID is required to be set up for each position ID oscillator and at the same time, a position coordinate should be stored in advance for each position ID of the mobile station. Since almanac and ephemeris are not updated while a mobile station stays indoors, the initial positioning time is delayed when the mobile station comes outdoors and can directly receive a GPS signal.
According to the above-mentioned technology disclosed in the document 2, it is necessary to store in advance the latitude and longitude data about the position of a transmission apparatus in this apparatus. Additionally, a receiver that can receive both the GPS signal and the latitude and longitude data in the mobile station is required. In the case where a GPS signal is received or the latitude and longitude data is received, the processing becomes complicated by adding a procedure for determining whether the position positioned by the GPS signal or the latitude and longitude data should be used. Furthermore, in the case where the position-positioning is implemented using the GPS signal that is re-transmitted, the GPS signal is not propagated through the original propagation path but through the re-transmission apparatus. Consequently, the accuracies of the positioning results sometimes become low since an error occurs on the attainment time of the GPS signal.
Even in the technology disclosed in either document 1 or 2, the latitude and longitude data that is stored in advance is transmitted to the mobile station in a GPS signal non-receipt area. Therefore, in the case where the GPS signal non-receipt area itself moves, for example, in the case where the GPS signal non-receipt area is an area in a car, a ship, an airplane, etc. and the terminal possessed by a person who is in the car, etc., is a mobile station, this technology cannot be used.
In the technology that is disclosed in the above-mentioned document 3, a mobile station can be promptly positioned when it comes into a position where the GPS signal can be directly received. However, in the case where the position-positioning is implemented using the GPS signal that is re-transmitted, the GPS signal is not propagated through the original propagation path but through the re-transmission apparatus. Consequently, the accuracies of the positioning results become low since an error occurs on the attainment time of the GPS signal.
In an apparatus for continuing a positioning operation for the own position in the GPS signal non-receipt area among the car navigation system, etc. using a gyrocompass, a direction sensor, a distance sensor, etc., the outputs of various kinds of sensors include errors so that the accuracies of the positioning results become low. Especially, in the case where the terminal possessed by a person is a mobile station, the output errors of such various kinds of sensors increase in accordance with the attitude and movement of the person so that the accuracies of the positioning results might further decrease.